CN1168249C - Self-adaptive threshold pseudo-random code catching and identifying method - Google Patents

Abstract

The present invention relates to a self-adaptive threshold pseudo-random code catching and identifying method, which is applied to spread spectrum communication. The present invention comprises the following steps that 1 I and Q data of a transmitting terminal can be transmitted to a receiving terminal after converted by jaff codes; the present invention is characterized in that the present invention also comprises the following steps that 2 received signals and local PN I and PN Q generated by a PN code can be calculated in a multiple correlation mode, and corresponding signal energy z1 of any phase 1 can be obtained after the coherent accumulation, the square addition taking energy and the noncoherent accumulation are carried out; 3 reference correlator estimation noise energy yn can be adopted; 4 the signal energy z1 and the noise energy yn can be compared and judged, and phases of a PN code generator can be controlled by judgment results; thereby, a code division multiple access system of a continuous pilot channel is provided.

Description

A kind of self-adaptive threshold pseudo-random code catching and substantive approach

The present invention relates to communication technical field, relating in particular to can synchronous a kind of self-adaptive threshold pseudo-random code catching and the substantive approach of acquisition time in spread spectrum communication.

In spread spectrum communication, receiver at first wants acquisition time synchronous, just makes the local frequency expansion sequence and the frequency expansion sequence phase alignment of transmission, and this is to be finished by catching of receiver.

In the forward link (from the base station to the travelling carriage) of CDMA (code division multiple access) cellular mobile communication, for the ease of the coherent detection of travelling carriage and chip (chip-level) level synchronously, in system design (comprising IS-95, CDMA2000, WCDMA), often all adopt the channel of continuous pilot.Travelling carriage just can be done PN sign indicating number (pseudo noise code) and catches on Common Pilot Channel like this.

According to the difference of base station spread spectrum structure, the PN sign indicating number arresting structure of travelling carriage is also corresponding to be changed to some extent.In 3G (Third Generation) Moblie, (comprise WCDMA and CDMA2000), all adopt the structure of multiple spread spectrum.

As shown in Figure 1, 2, wherein, Fig. 1 is the structural representation of multiple spread spectrum, and Fig. 2 is the arresting structure schematic diagram of travelling carriage on pilot channel.

Corresponding pilot channel, data I=1, Q=0, (seeing Fig. 1,2), like this, the arresting structure of travelling carriage on pilot channel is as shown in Figure 2.With signal and the local PN that receives _IAnd PN _QCarry out the multiple correlation computing, after getting energy, noncoherent accumulation, obtain certain phase place 1 pairing energy z through coherent accumulation, quadratic sum ₁, then with z ₁Compare with a decision threshold, result relatively delivers in the Search Control module and adjudicates, and local PN (pseudorandom) sequence just under the effect of Search Control module, constantly changes the phase place of local PN sequence, up to thinking that frequency expansion sequence is synchronous.

For receiver, capture time and acquisition probability are two important indicators of weighing acquisition performance.And lower signal to noise ratio, Doppler frequency shift, channel fading etc. all are the key factors that influences the travelling carriage receptivity.In this case, harvesting policy commonly used at present has:

(1). maximum likelihood method

Maximum likelihood method is the best method that overcomes channel fading, improves acquisition performance.It selects the pairing phase place of maximum related value as candidate's phase place at the enterprising line search of whole PN code phase then.This method is owing to need search for all PN code phases, and capture time just is directly proportional with the PN code length like this, and when the PN sign indicating number is longer (as CDMA2000), capture time just can not satisfy the requirement of system.If adopt many correlators parallel source/catching structure, can shorten capture time, but the relevant hardware resource increases, system will be very complicated and unacceptable.

(2). serial search, threshold judgement method

This is a kind of in the method that averages out aspect capture time and the acquisition probability two.It is with current correlation z ₁Compare with decision threshold, if z ₁Surpass decision threshold, just think that current phase place is candidate's phase place, when adopting this method, the setting of thresholding is very big to Effect on Performance.

Two kinds of thresholding setting methods are arranged usually: fixed threshold and adaptive threshold.The method of fixed threshold can not satisfy the needs of signal to noise ratio dynamic change in actual applications, so poor-performing; The key of adaptive threshold method is to estimate current noise energy exactly, thereby obtains corresponding decision threshold.Employing can obtain decision threshold more accurately with reference to the correlator estimated noise energy, but this method requires to produce in this locality and the used spreading code of the received signal PN sign indicating number of quadrature mutually, seeks the design complexities that such code word has increased receiver.

(3). catch confirmation

In actual applications, in order to reduce the false alarm probability of catching, reduce capture time.Need do further confirmation to the possible phase place that surpasses decision threshold.Traditional confirmation strategy probably can be divided into two kinds: correlation is repeatedly adjudicated and two pause the (pause) confirmation more.

Correlation is repeatedly adjudicated confirmation be meant that its result compares with adaptive threshold to carrying out inferior related operation again above possible candidate's phase place of decision threshold again, wait until that the number of times that surpasses decision threshold that comparison module is sent is added to N _MinAfter inferior, think that just candidate's phase place is a locking phase, thus the tracking mode of entering, N _MaxAnd N _MinIt is the parameter that system pre-sets.

Two pauses (pause) confirm to be meant the related operation that possible candidate's phase place is carried out again N time on the longer time more, if this correlated results of N time has all surpassed decision threshold separately, think that just candidate's phase place is a locking phase.

These two kinds tradition confirm that the common features of strategy all are only to have utilized adaptive threshold information, like this acquisition performance of whole system just with accuracy, the parameter N of decision threshold _MaxAnd N _MinSelection and pause times N very big relation is arranged, at this moment resulting performance improvement often just has bigger difference under different conditions.

The object of the present invention is to provide a kind of self-adaptive threshold pseudo-random code catching and substantive approach, it can be applicable to that transmitting terminal adopts multiple spread spectrum, and has the cdma system of continuous pilot channel.

The object of the present invention is achieved like this:

A kind of self-adaptive threshold pseudo-random code catching and substantive approach, it is applied to comprise step in the broadband communication:

(1). I, the Q data of transmitting terminal are delivered to receiving terminal after changing through multiple scrambler;

Its characteristics are, and are further comprising the steps of:

(2). with signal that receives and the local PN that produces by the PN code generator _IAnd PN _QCarry out the multiple correlation computing, after getting energy, noncoherent accumulation, obtain certain phase place 1 pairing signal energy z through coherent accumulation, summed square ₁

${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C0013171100131.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1=\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\left[(\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}R\left(t\right)\&CenterDot;({\mathrm{PN}}_I(n+(k-1)N)-j\&CenterDot;{\mathrm{PN}}_Q(n+(k-1)N){)}^2\right]-------\left(2\right)$

Wherein, R (t) is a received signal, and N is the number of times of coherent accumulation;

(3). adopt with reference to correlator estimated noise energy y _n

(4). to signal energy z ₁With noise energy y _nCompare judgement, and according to the phase place of judged result control PN code generator, method is as follows:

A., the initial value that one signal energy maximum Zmax confirms judgement is set, then with signal energy z ₁With noise energy y _nCompare judgement;

If signal energy z b. ₁Greater than noise energy y _n, then current phase place 1 is exactly possible candidate's phase place, at this moment enters the phase place validation process, and this phase place is carried out Z _MaxConfirm to judge;

If N c. _MaxSignal energy z in the inferior judgement ₁Greater than (1-y) * Z _MaxNumber of times greater than N _MinInferior, just think that candidate's phase place 1 is locking phase, finishes thereby catch, wherein Z _MaxBe the historical maximum of corresponding energy, y is for adjusting coefficient;

If N d. _MaxSignal energy z in the inferior judgement ₁Greater than (1-y) * Z _MaxNumber of times smaller or equal to N _MinInferior, just think that candidate's phase place 1 is asynchronous phase place, and make Z _Max=max (z1, Z _Max), then judge next phase place;

If e. signal energy z1 is less than or equal to noise energy yn, then make Zmax=max that (z1 Zmax), then judges next phase place.

In a kind of self-adaptive threshold pseudo-random code catching and substantive approach of the above, wherein, in described step (3), described employing is with reference to correlator estimated noise energy y _nBe directly with the I, the Q signal that receive with connect instead after PN _IAnd PN _QCarry out related operation, get energy and obtain estimated noise energy y through coherent accumulation, summed square again _n

${\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="C0013171100131.png"\; state="\{\{state\}\}">E</figure-callout>}}_1=\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\left[(\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}R\left(t\right)\&CenterDot;({\mathrm{PN}}_Q(n+k-1)N)-j\&CenterDot;{\mathrm{PN}}_I(n+(k-1)N)){)}^2\right]-------\left(3\right)$

In a kind of self-adaptive threshold pseudo-random code catching and substantive approach of the above, wherein, in described step (3), with the noise energy y that obtains _nCarry out filtering, to obtain more stable noise energy estimated value y _n

In a kind of self-adaptive threshold pseudo-random code catching and substantive approach of the above, wherein, Alpha's filtering is adopted in described filtering, and the value of filter coefficient alpha is greater than 0.9.

y _n＝(1-a)·E _l+a·y _n-1 (4)

A kind of self-adaptive threshold pseudo-random code catching of the present invention and substantive approach owing to adopted above-mentioned technical scheme, make it compared with prior art have following advantage and good effect:

(1). noise energy is estimated accurately.

The present invention is because in the design of CDMA air interface, in order to reduce the phase mutual interference between I, the Q two-way, selected PN _IAnd PN _QBetween all have good orthogonality, receiving terminal just can utilize these characteristics to obtain the accurate valuation of noise energy easily like this, and this method need not produce the code word with received signal spreading code quadrature in this locality, therefore simplify the design of receiver.

(2). adaptive threshold is adjudicated method and maximum likelihood method combines.

The present invention is owing to be designed to work as operation of receiver at low signal-to-noise ratio, when being subjected to the influencing of Doppler frequency shift, channel fading and other bursty interference simultaneously, just there is bigger limitation in the application of threshold method itself, at this moment be a kind of more reasonably selection to the confirmation of carrying out maximum likelihood above the possible phase place of decision threshold, we are example with the method for correlation repeatedly being adjudicated confirmation, can design like this to catch to confirm strategy: possible candidate's phase place is carried out N again _MaxInferior related operation will be multiplied by historical maximum and resulting N behind the proportionality coefficient in comparison module _MaxIndividual correlation compares, and is added to N if surpass the number of times of this maximum likelihood threshold value _MinInferior, think that just candidate's phase place is a locking phase, thus the tracking mode of entering, N _MaxAnd N _MinIt is the parameter that system pre-sets.

(3). the present invention has avoided the phase place of whole PN sign indicating number is searched for owing to only the possible phase place that surpasses decision threshold is just adopted the repeatedly confirmation of maximum likelihood, has shortened capture time greatly.

(4). this adaptive threshold of the present invention catch substantive approach can also be with two pauses, pause more, many correlators parallel source/catching structure combine, and satisfies different needs, has very big flexibility.

By following a kind of self-adaptive threshold pseudo-random code catching of the present invention is combined the description of its accompanying drawing with an embodiment of substantive approach, can further understand purpose of the present invention, concrete technical characterictic and advantage.Wherein, accompanying drawing is:

Fig. 1 is the structural representation of multiple spread spectrum in the mobile communication of prior art;

Fig. 2 is the travelling carriage pilot signal synchronization acquistion schematic diagram of prior art;

Fig. 3 is that the realization theory diagram is caught in a kind of self-adaptive threshold pseudo-random code catching of the proposition according to the present invention and the main footpath of substantive approach;

Fig. 4 is a thresholding comparison search control module judgement flow chart in a kind of self-adaptive threshold pseudo-random code catching that proposes of the present invention and the substantive approach.

As shown in Figure 3, this is the main realization theory diagram of directly catching of a kind of self-adaptive threshold pseudo-random code catching of the present invention and substantive approach.The present invention, a kind of self-adaptive threshold pseudo-random code catching and substantive approach, it is applied to may further comprise the steps in the broadband communication:

The first step is delivered to receiving terminal after the multiple scrambler conversion of I, Q data process with transmitting terminal, and received signal is expressed as:

R(t)＝(I+j·Q) (1)

Second step is with signal that receives and the local PN that is produced by the PN code generator _IAnd PN _QCarry out the multiple correlation computing, after getting energy, noncoherent accumulation, obtain certain phase place 1 pairing signal energy z through coherent accumulation, summed square ₁, wherein, N is the number of times of coherent accumulation, M is the number of times of noncoherent accumulation;

${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C0013171100131.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1=\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\left[(\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}R\left(t\right)\&CenterDot;({\mathrm{PN}}_I(n+(k-1)N)-j\&CenterDot;{\mathrm{PN}}_Q(n+(k-1)N){)}^2\right]-------\left(2\right)$

In the 3rd step, adopt with reference to correlator estimated noise energy y _n, to obtain decision threshold, in this step, we still adopt the way that produces decision threshold with reference to correlator, and, with receiver local produce method with the mutually orthogonal code word of PN sign indicating number that receives different be: we utilize the characteristics and the PN of multiple spread spectrum _IAnd PN _QBetween good orthogonality, directly with the I, the Q signal that receive with connect instead after PN _IAnd PN _QCarry out related operation, get through coherent accumulation, summed square again that energy obtains;

$Z_t=\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\left[(\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}R\left(t\right)\&CenterDot;({\mathrm{PN}}_I(n+(k-1)N)-j\&CenterDot;{\mathrm{PN}}_Q(n+(k-1)N){)}^2\right]-------\left(2\right)$

And, with the noise energy y that obtains _nCarry out filtering, to obtain more stable noise energy estimated value y _n, usually, Alpha's filtering is adopted in described filtering, and the value of this Alpha's filter coefficient alpha is greater than 0.9.

y _n＝(1-a)·E _l+a·y _n-1 (4)

The 4th step is to signal energy z ₁With noise energy y _nCompare judgement, and control the phase place of PN code generator according to judged result.(see figure 4).

As shown in Figure 4, this is a thresholding comparison search control module judgement flow chart in the substantive approach of a kind of self-adaptive threshold pseudo-random code catching of the present invention.In the 4th step, to signal energy z ₁With noise energy y _nCompare judgement, and according to the phase place of judged result control PN code generator, it may further comprise the steps:

A., the initial value that one signal energy maximum Zmax confirms judgement is set, then with signal energy z ₁With noise energy y _nCompare judgement;

If signal energy z b. ₁Greater than noise energy y _n, then current phase place 1 is exactly possible candidate's phase place, at this moment enters the phase place validation process, and this phase place is carried out Z _MaxConfirm to judge;

If N c. _MaxSignal energy z in the inferior judgement ₁Greater than (1-y) * Z _MaxNumber of times greater than N _MinInferior, just think that candidate's phase place 1 is locking phase, finishes thereby catch, wherein Z _MaxBe the historical maximum of corresponding energy, y is for adjusting coefficient;

If N d. _MaxSignal energy z in the inferior judgement ₁Greater than (1-y) * Z _MaxNumber of times smaller or equal to N _MinInferior, just think that candidate's phase place 1 is asynchronous phase place, and make Z _Max=max (z1, Z _Max), then judge next phase place;

If e. signal energy z1 is less than or equal to noise energy yn, then make Zmax=max that (z1 Zmax), then judges next phase place.

If false phase place is passed through N _MaxInferior confirmation can be got rid of interference, has improved Z simultaneously _Max, like this in the maximum likelihood of possibility phase place confirms next time, because Z _MaxRaising, false alarm probability is further descended.And for those correct phase places, according to maximum likelihood principle, its correlation must be maximum, and maximum related value has N like this _MinInferiorly surpass proportionality coefficient to be multiplied by its historical peaked possibility be very big, thereby fully guaranteed acquisition probability.

In sum, a kind of self-adaptive threshold pseudo-random code catching of the present invention and substantive approach are compared and are had following characteristics and advantage with traditional substantive approach of catching:

1) the present invention produces adaptive decision threshold owing to adopt independent reference correlator estimated noise energy. The local PN code phase that adopts when the reference correlator when receiving signal PN code phase and keep quadrature, relevant output The result is exactly the accurate estimation to noise. We connect I, Q two-way instead in realization, and its output is passed through again like this Just can obtain behind Alpha's wave filter relatively accurately and the estimated value of noise energy stably. This method realizes letter Single, the accuracy that noise is estimated is higher, under different signal to noise ratio environment good adaptability is arranged.

2) in order to guarantee that under varying environment, acquisition algorithm all has preferably performance, the low noise in the antagonism communication Ratio, Doppler frequency domain, channel fading and the unexpected error that may occur, the present invention can to what surpass the thresholding valuation Candidate's phase place of energy is carried out the repeatedly confirmation of maximum likelihood again. If candidate's phase place is correct phase place, according to maximum Likelihood criterion has N_minInferior is very big above its historical peaked possibility, thereby has fully guaranteed acquisition probability. For the phase place of falseness, pass through N_maxInferior confirmation can be got rid of interference, has improved simultaneously Z_max, like this in the maximum likelihood of possibility phase place confirms next time, because Z_maxRaising, false-alarm probability is further descended. This Confirm that strategy is more reasonable with respect to the method that traditional and decision threshold repeatedly compare, take full advantage of maximum seemingly Right characteristic realizes also very simply, and adopts maximum likelihood to confirm Parameter N_minAnd N_maxSelection also compare Flexibly.

3) the present invention adopts serial search, threshold judgement, thus avoided all phase places are searched for judgement, big Shortened greatly capture time. This method can also organically combine with many correlators parallel source/catching structure, advances one Step shortens capture time.

4) the confirmation strategy of this maximum likelihood of the present invention can also be applied to the catching methods such as two pauses, many pauses In, have stronger technical compatibility.

Claims (4)

1. self-adaptive threshold pseudo-random code catching and substantive approach, it is applied to comprise step in the broadband communication:

(1). I, the Q data of transmitting terminal are delivered to receiving terminal after changing through multiple scrambler;

It is characterized in that, further comprising the steps of:

(2). with signal that receives and the local PN that produces by the PN code generator _IAnd PN _QCarry out the multiple correlation computing, after getting energy, noncoherent accumulation, obtain certain phase place 1 pairing signal energy z through coherent accumulation, summed square ₁

(3). adopt with reference to correlator estimated noise energy y _n

(4). to signal energy z ₁With noise energy y _nCompare judgement, and according to the phase place of judged result control PN code generator, method is as follows:

A., the initial value that one signal energy maximum Zmax confirms judgement is set, then with signal energy z ₁With noise energy y _nCompare judgement;

If signal energy z b. ₁Greater than noise energy y _n, then current phase place 1 is exactly possible candidate's phase place, at this moment enters the phase place validation process, and this phase place is carried out Z _MaxConfirm to judge;

If N c. _MaxSignal energy z in the inferior judgement ₁Greater than (1-y) * Z _MaxNumber of times greater than N _MinInferior, just think that candidate's phase place 1 is locking phase, finishes thereby catch, wherein Z _MaxBe the historical maximum of corresponding energy, y is for adjusting coefficient;

If N d. _MaxSignal energy z in the inferior judgement ₁Greater than (1-y) * Z _MaxNumber of times smaller or equal to N _MinInferior, just think that candidate's phase place 1 is asynchronous phase place, and make Z _Max=max (z1, Z _Max), then judge next phase place;

If e. signal energy z1 is less than or equal to noise energy yn, then make Zmax=max that (z1 Zmax), then judges next phase place.

2. a kind of self-adaptive threshold pseudo-random code catching as claimed in claim 1 and substantive approach is characterized in that: in described step (3), described employing is with reference to correlator estimated noise energy y _nBe directly with the I, the Q signal that receive with connect instead after PN _IAnd PN _QCarry out related operation, get through coherent accumulation, summed square again that energy obtains.

3. a kind of self-adaptive threshold pseudo-random code catching as claimed in claim 1 and substantive approach is characterized in that: in described step (3), with the noise energy y that obtains _nCarry out filtering, to obtain more stable noise energy estimated value y _n

4. as claim 1 or 3 described a kind of self-adaptive threshold pseudo-random code catching and substantive approaches, it is characterized in that: Alpha's filtering is adopted in described filtering, and the value of filter coefficient alpha is greater than 0.9.

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